Saying used (especially in the southern US) when the sun is shining yet it's raining. I've been told that in Scandinavian countries they say "There's a marriage in Hades" for this, and in South America they say "The devil and his wife are dancing." (Since all version relate to the devil and his spouse, there's probably some older story that all these sayings derive from.)
I wanna know, have you ever seen the rain, coming down on a sunny day? Yes, the devil is beating his wife. (Heh, CCR reference too.)
When the sun is shining but it's raining at the same time.
Adam: Look Jane! It's raining and there's sun at the same time.
Jane: The devil is beating his wife, adam.
Adam: Silly bastard!